Monolithic switching power supply design

Switching power supplies have outstanding advantages such as high efficiency, light weight, small size, and wide voltage stabilization range. Since their advent in the mid-20th century, they have developed extremely rapidly and have been widely used in computers, communications, aerospace, offices, and household appliances. It has great potential to replace linear regulated power supply. Improving circuit integration is one of the pursuits of switching power supplies. For small and medium power switching power supplies, it is to achieve monolithic integration. The switching integrated voltage regulator refers to the integration of the control circuit, power switch tube and protection circuit into one chip, and the switching power supply composed of the switching integrated voltage regulator is called a monolithic switching power supply. The monolithic switching power supply series of the American PI Company is its outstanding representative.
The 250W switching power supply circuit designed by TOPSwitch—GX is shown in Figure 1. The DC voltage is added to the drain D of TOPSwitch-GX through the primary side of the transformer; the frequency selection terminal F and the limit current setting terminal X are connected to the source S, then the functions of both ends are useless, that is, the limit is not set externally. Current, the self-protection current ILIMIT is automatically set internally, and the switching operating frequency is 132K; the control pole is connected to the optocoupler LTV817 and receives feedback signals to control the duty cycle of the internally integrated high-voltage power MOS tube; the line detection terminal L passes through a 2MΩ The resistor is connected to the positive terminal of the DC high-voltage input to realize line voltage detection of overvoltage and undervoltage line voltage feedforward. Capacitor C1 is a high-frequency filter capacitor; the transient voltage suppressor P6KE200 and the ultra-fast recovery diode BYV26C form a clamping circuit, and an RC absorption circuit (composed of R2, R3 and C6) is connected in series to it, so that in addition to absorbing part of the leakage inductance In addition to the energy in the circuit, the voltage can also be clamped at 200V, so that the drain voltage of the TOPSwitch-GX internal integrated MOS tube does not exceed 700V when the switching power supply is started or overloaded; the secondary output of the high-frequency transformer T1 passes through the MURl640CT After rectification and C9, C10 and C11 filtering, and then filtering the switching noise through magnetic beads L1 and C12, the output voltage is obtained; VD4 and C14 form a soft-start circuit.
The monolithic switching power supply has significant advantages such as monolithic integration, simpler peripheral circuits, better performance indicators, and the ability to achieve complete isolation without power frequency transformer electrical appliances. It is an ideal choice for us to design switching power supplies below 290W.